1. Verb - to press up against or to jostle.
2. Noun - the end part of a rifle or shotgun or machinegun that rests against the shoulder or pectoral muscles to increase stability during firing.
3. Noun - the part of a human being that knows wind and earth. The buttocks and anus of a person.
4. Noun - the recipient or target of a joke.

Ever since Father O'Malley was caught butting that butt into that young choirboy's butt, he has become the butt of many cruel jokes.

an extra face on your rear end that has two cheeks and a mouth but no nose eyes or ears. This mouth spits out the remaindence of what you ate for lunch that your body didn't use to get good stuff from.